1. Field of Invention
This invention relates to exposing a photoreceptor to fluorescent light in order to attenuate the effects of positive over-spray on the photoreceptor.
2. Description of Related Art
In xerography, or electrophotographic printing/copying, a charge-retentive device called a photoreceptor is electrostatically charged, and then exposed to a light pattern of an input image to selectively discharge the surface in accordance with the image. The resulting pattern of charged and discharged areas on the photoreceptor forms an electrostatic charge pattern, i.e., a latent image, conforming to the input image. The latent image is developed by contacting it with finely divided electrostatically attractable powder called toner. Toner is held on the image areas by the electrostatic force. The toner image may then be transferred to a substrate or support member, and the image is then affixed to the substrate or support member by a fusing process to form a permanent image thereon. After transfer, excess toner left on the photoreceptor is cleaned from its surface and residual charge is erased from the photoreceptor.
In systems where both the photoreceptor and the toner are negatively charged, the latent image is also negatively charged. During transfer, the substrate or support member is brought into contact with the photoreceptor, covering the toner image, and is sprayed with positive ions. This enables the negatively charged toner image to transfer from the photoreceptor to the substrate or support member. For optimal image production, the photoreceptor should be uniformly charged across its entire surface.
Multilayered organic photoreceptors are generally designed to work in negative charging mode. During transfer, locations on the photoreceptor surface that are not covered by the substrate or support member are exposed to the spray of positive ions. This phenomenon will herein be referred to as xe2x80x9cpositive over-spray.xe2x80x9d The present inventors have discovered that positive over-spray has a negative impact on the performance of multilayered organic photoreceptors. Specifically, transfer corotron positive over-spray results in localized high dark decay on the photoreceptor and consequently voltage non-uniformity.
In subsequent cycles of the xerographic process, the portion of the photoreceptor surface that received the positive charge due to positive over-spray will have a different exposure potential than the portion of the photoreceptor surface that was covered by the substrate or support member and thus was not exposed to the positive charge. This difference in exposure potential inhibits the ability to uniformly negatively charge the photoreceptor. The portion of the photoreceptor that is exposed to the positive over-spray cannot retain the negative charge as well as the portions of the photoreceptor that were not exposed to the positive over-spray.
The more positive charge that is involved in transfer, the more exaggerated the above-mentioned problems tend to be. For example, both heavy weight paper and humidity conditions require more positive charge for efficient image transfer, and thus result in significant photoreceptor charge non-uniformity and a significant decrease in photoreceptor charge retention. Xerographic process control can be made difficult and the customer could detect the effects (e.g., undesirable print marks) when changing paper size or pitch mode. These problems occur regardless of the type of image. For example, these problems occur in both halftone and full color image copying/printing.
The present inventors have discovered that after transfer and after the substrate or support member has been separated from the photoreceptor, but before charging of the photoreceptor for the next cycle in the xerographic process, exposure of the photoreceptor to fluorescent light at least attenuates the problems associated with positive over-spray. The fluorescent light exposure can bring a positive-charge-induced non-uniformity signal down to a non-printable level.
These and other features and advantages of the invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.